The heat sink is a requisite component used to deal with the heat-dissipating problem in various electronic devices for a long time. Take the power supply of a liquid crystal display or notebook as an example; the electronic components disposed on the printed circuit board (PCB) include the capacitor, resistor, inductor, transformer, diode, metal oxide semiconductor field effect transistor (MOSFET), die, and so on. When the power supply is operated, these electronic components will produce heat at different levels. If the heat cannot be dissipated efficiently, the electronic components will be out of order due to the overheated condition, and even more, the whole system might shut down. Therefore, the heat sink is an important component to the power supply for solving the heat-dissipating problem thereof.
For dissipating heat in an efficient way, the heat sink is usually attached on the high power component such as the chip. Due to the limitation of the circuit layout and the space arrangement, the high power transistor can be secured on the heat sink that is fixed on the printed circuit board, so that a heat-dissipating area can be provided in the direction perpendicular to the printed circuit board for dissipating the heat of the transistor. Please refer to FIG. 1, which is a schematic diagram showing a conventional structure for fixing the heat sink on the printed circuit board. As shown in FIG. 1, the fixing device 2 is disposed at the bottom of the heat sink 1 for fixing the heat sink 1 on the printed circuit board 3. The fixing device 2 of the heat sink 1 comprises a connecting portion 21 and a pin 22, wherein the connecting portion 21 is riveted on one side at the bottom of the heat sink 1 and the pin 22 is extended downward from the lower edge of the connecting portion 21. When the heat sink 1 is to be fixed on the printed circuit board 3, the pin 22 of the fixing device 2 is plugged into the corresponding pinhole 31 on the printed circuit board 3. Then, the heat sink 1 is secured on the printed circuit board 3 after the tin soldering process.
The fixing device 2 of the heat sink 1 is often made of a thin metal plate in order to increase usable space for the printed circuit board 3. However, since the heat sink 1 has a certain weight, in the processes of assembling, delivering or using, the fixing device 2 may become deformed and thus fails to carry the heat sink 1 efficiently if the mechanical strength of the pin 22 is not strong enough or the soldering area of the pin 22 is too small to secure the heat sink 1 on the printed circuit board 3 well. Further, the shaking force may be passed to the transistor (not shown) secured on the heat sink 1 through the fixing device 2, resulting in the break of the pins of the transistor which are plugged onto the printed circuit board 3. Moreover, the aforesaid force may also be passed to the printed circuit board 3 through the pins of the transistor, resulting in the damage of the copper foil on the printed circuit board 3 or the break of the solder ball between the pin 22 of the fixing device 2 and the printed circuit board 3. The above conditions may cause the collapse of the heat sink 1, and further result in a bad connection or even short circuit of the printed circuit board 3.
Therefore, it is required to develop a fixing device that can fix the heat sink on the printed circuit board firmly.